Torsional vibrations resulting from speed oscillations in an internal combustion engine are common and lead to excessive noise and reduced gear life, which in turn, may cause premature engine failure. The oscillations are produced by various torques applied to components within the engine, such as a crankshaft or camshaft, during normal operation of the engine. For example, the torque applied to the camshaft is constantly varied from a high torque when the springs of the intake and exhaust valves and the unit injectors are being compressed to a low torque when the springs of the valves and unit injectors are expanded. The high torque applied to the camshaft causes the camshaft to twist until the valves and injectors are totally compressed. Shortly after the valves and injectors have reached the maximum compressive state, the camshaft instantaneously backlashes due to relinquishing the forces stored during twisting. The wide range of torques applied to the camshaft induce oscillations resulting in increased dynamic loading on the gear train, increased torsional vibrations, excessive noise, and reduced gear life.
It is known in the art that crankshaft vibration can be reduced by increasing the flywheel inertia, increasing the compliance of the driveline, or adding dissipative devices in the driveline. For example, rotating pendulum vibration absorbers have been used which include a carrier mounted to the crankshaft. The carrier has bores that contain cylindrical rollers that are retained within the bores yet are free to move within the bores. As the crankshaft and carrier rotate the rollers are subject to centrifugal forces which attempt to position the rollers at the outer radius of the carrier bores. As speed increases, the centrifugal force increases resulting in a natural frequency of the roller within the carrier that changes in direct proportion to the speed. This allows the pendulum absorbers to be tuned for a given multiple of the crankshaft speed and the ability to maintain this effective tuning throughout the engine's speed range. Any oscillations occurring at this multiple of engine speed cause the rollers to oscillate in their bores which in turn creates a torque which opposes the original oscillations and thereby reduces crankshaft vibration.
It is also known that camshaft vibration can be reduced by using rubber or spring devices. U.S. Pat. No. 5,017,178 issued to Roger D. Krikke, et al. discloses a coupling apparatus for resiliently transmitting torque including a pin assembly positioned in mechanical connection between an annular plate member and a gear member. The apparatus also dampens backlash motion by utilizing the pin assembly and a mechanism for biasing a piston into contact with the annular plate member. The coupling apparatus actually isolates the torsional vibrations of the camshaft from the camshaft gear in order to protect the gear train from excessive loading but does not seek to resolve the torsional vibrations of the camshaft. In addition, the coupling apparatus requires extensive machining making the apparatus uneconomical to produce in large quantities.
The art as cited above does not recognize a further problem in that the recent development of camshaft actuated high pressure unit injectors has drastically increased the torques applied to the camshaft. This problem is further magnified by the non-linear dynamic behavior of gear trains which by common design practice contain zones of relative motion without any torque transmittal. The highly varied applied camshaft torques can be significantly increased due to the impactive type loading on the gears and bearings within the gear train during reversals in motion. Additionally, as engine emission laws become more stringent, the need to maintain the proper timing of the valving and injector events relative to the crankshaft and piston position becomes more critical. The trend toward producing the high pressure unit injector engines makes it increasingly necessary to produce an economical method to reduce camshaft vibration.
The present invention is directed to overcoming one or more of the problems as set forth above.